Quaternary ammonium hydroxides such as tetramethylammonium hydroxide (TMAH) and tetraethyl ammonium hydroxide CTEAH) are strong organic bases that have been known for many years. Such quaternary ammonium hydroxides have found a variety of uses including use as titrants for acids in organic solvents and as supporting electrolytes in polarography. Aqueous solutions of quaternary ammonium hydroxides, particularly TMAH solutions, have been used extensively as a developer for photoresists in printed circuit board and microelectronic chip fabrication. Use of quaternary ammonium hydroxides in the electronics area requires that there be no residue following the normal post-bake period. In electronic applications, it is desirable that the aqueous solutions of quaternary ammonium hydroxides should be essentially free from metal ions such as sodium, potassium, zinc and calcium; anions such as halides, nitrates, nitrites, carbonates, carboxylates, sulfates and neutral organic species such as methanol, amines, etc. Particularly in recent years, there has been an increasing demand for quaternary ammonium hydroxides having a high purity.
Quaternary ammonium hydroxides also are useful as reagents for removing hydrohalide impurities from quaternary ammonium salt reaction products thereby providing metal-free, hydrohalide-free quaternary ammonium salts; as intermediates for synthesizing quaternary ammonium salts by neutralization with appropriate acids; as solubilizers for anions in organic solutions (e.g., phase transfer catalysts); as templating agents for zeolites; as supporting electrolytes in electroorganic synthesis and electroanalysis; as cleaning agents for electronic circuits; and as strong base catalysts.
A number of prior art patents describe the preparation of quaternary ammonium hydroxides by electrolyzing a salt of a quaternary ammonium compound. U.S. Pat. Redesign 32,398 (DeWitt et at) describes an electrolytic process for removing the anion from quaternary organic salts. The process uses a cell comprising four compartments containing two cation exchange membranes defining the cathode and anode compartments and an anion exchange membrane dividing the space between the two cation exchange membranes into two inner compartments. The quaternary organic salt is charged to the inner compartment which is adjacent to the catholyte compartment and is thus separated from the catholyte compartment by the cation exchange membrane. Water is charged to the other three compartments and a small amount of an electrolyte is also charged to the anolyte compartment. On passage of a current, the quaternary cation passes through the cation exchange membrane into the catholyte compartment and a hydroxide ion is formed resulting in the formation of a quaternary hydroxide in the catholyte compartment. The anion of the salt passes through the anion exchange resin into the inner compartment which is adjacent to the catholyte anolyte compartment. In this process, the quaternary organic hydroxide is recovered from the catholyte compartment and an inorganic acid is recovered from the inner compartment adjacent to the anolyte compartment.
U.S. Pat. No. 3,402,115 (Campbell et al) describe the preparation of quaternary ammonium hydroxides from a bis-quaternary ammonium sulfate in an electrolytic cell containing three chambers. The three chambers include an anolyte chamber containing an anode, a catholyte chamber containing a cathode, and a chamber containing a bis-quaternary ammonium sulfate salt positioned between the anolyte and catholyte chambers. The salt containing chamber is separated from the anolyte chamber by an anion exchange resin membrane, and is separated from the catholyte chamber by a cation exchange resin membrane. An aqueous sulfuric acid solution is continuously circulated through the anolyte chamber, and a dilute aqueous quaternary ammonium hydroxide solution is continuously circulated through the catholyte chamber. When an electric potential is applied, sulfate ions migrate through the anion exchange membrane into the anolyte chamber, and quaternary ammonium ions migrate through the cation exchange membrane into the catholyte chamber. The quaternary ammonium hydroxide product is obtained by withdrawing a portion of the aqueous solution from the catholyte chamber.
U.S. Pat. No. 5,286,354 (Bard et al) describe a method of preparing organic and inorganic hydroxides and alkoxides from the corresponding halide salts in a two-compartment divided cell. The desired compounds are formed in the catholyte while the accumulation of halogen in the anolyte is effectively prevented through the action of a reducing agent added to the acidic anolyte solution.
Copending application Ser. No. 08/148,925, filed Nov. 8, 1993, describes the process for preparing organic and inorganic hydroxides or alkoxides and for improving the purity of organic and inorganic hydroxides or alkoxides utilizing a three-compartment electrolysis cell. The electrolysis cell comprises an anolyte compartment containing an anode, a catholyte compartment containing a cathode in water, and at least one intermediate compartment containing water, an organic liquid, or a mixture of water and an organic liquid, said at least one intermediate compartment being separated from the anolyte and catholyte compartments by at least two dividers selected from nonionic dividers, cation selected membranes, or combinations thereof. A mixture comprising an organic or inorganic hydroxide and an oxidizable liquid is charged to the anolyte compartment and a current is passed through the electrolysis cell to produce the purified organic or inorganic hydroxide in the catholyte compartment which is then recovered from the catholyte compartment.
Japanese Kokai Patent No. 60-131985 (1985) Crakahashi et at) describes a method of manufacturing a high purity quaternary ammonium hydroxide in an electrolysis cell which is divided into an anode chamber and a cathode chamber by a cation exchange membrane. A quaternary ammonium hydroxide solution containing impurities is charged to the anode chamber and a direct current is supplied between two electrodes after water has been charged to the cathode chamber. Purified quaternary ammonium hydroxide is obtained from the cathode chamber. The purified quaternary ammonium hydroxide contains reduced amounts of alkali metals, alkaline earth metals, anions, etc.
Japanese Kokai Patent No. 60-131986 (1985) Crakahashi et al) describes a method for manufacturing a high purity quaternary ammonium hydroxide. The method described in this patent utilizes an electrolysis cell which has been compartmentalized into an anode chamber, a cathode chamber, and at least one intermediate chamber with at least two cation exchange membranes. An aqueous solution containing a quaternary ammonium salt is charged to the anode chamber, water is charged to the cathode chamber, and an aqueous hydroxide solution corresponding to the quaternary ammonium salt charged into the anode chamber is charged into the intermediate chamber. Upon application of a direct current, a quaternary ammonium hydroxide is formed in the cathode chamber and recovered.
Japanese Kokai Patent No. Hei 2[11990]129390 describes a method of preparing quaternary ammonium hydroxide from a quaternary ammonium salt. The method described in this patent utilizes an electrolysis cell which has been compartmentalized into an anode chamber, a cathode chamber and an intermediate chamber. The intermediate chamber is separated from the cathode chamber by a cation exchange membrane, and the intermediate compartment is separated from the anolyte compartment by an anion exchange membrane. An aqueous solution containing a quaternary ammonium salt is charged to the intermediate chamber and water is charged to the cathode and anode chambers. Upon application of a direct current, quaternary ammonium hydroxide is formed in the cathode compartment and recovered. An acid is formed in the anode compartment.